The present invention relates to a reproducing system for magnetically recorded information, in particular, relates to such a system which reads out magnetically recorded information using an optical technique.
Conventionally, magnetically recorded information, recorded for instance on a magnetic tape, a magnetic disc, or a magnetic sheet, is read out by a magnetic head which has a magnetic core with a thin gap and a coil wound on said core. A magnetic head operates on the principle that the relative movement of the head to the recording medium generates electromotive force on the coil according to the recorded information.
However, that conventional magnetic head has the disadvantage that the recording density on a recording medium cannot be so high. They say that a conventional magnetic head needs a recording track wider than 30 .mu.m.
In order to solve the above problem, one of the solutions is an optical head which reads out magnetically recorded information using an optic-magnetic effect or the Faraday effect. According to that optical head, a soft magnetic film which has a magnetically soft nature having the easy magnetization axis in the thickness direction of the film contacts with a recording medium which records information magnetically, and the vertical component of the magnetically recorded information on the recording medium is copied on that soft magnetic film. The information on the soft magnetic film is read out optically using the Faraday effect in which an optical beam is subject to the rotation of the polarization plane according to the magnetic direction of a magnetic domain of that soft magnetic film. As the Faraday effect is used, an optical polarizer and an optical analyzer are usually used to detect the optical rotation of polarized optical beam.
However, a prior optical head has the disadvantage that it takes a long time to read out magnetically recorded information, since only a single bit on a soft magnetic film is read out at a time by illuminating said film with a thin spot of a laser beam. When a high speed read out is requested, a recording medium must run faster, but the improvement of the read out speed by high speed running the recording medium is not large.